Method for reproduction of a compnent with a micro-joint and component produced by said method

ABSTRACT

The method for production of a component with a micro-joint comprises a first step of deposition of a layer of polymer designed to constitute an assembly joint on a transfer substrate, a second step of bringing the polymer layer into contact with a micro-structured substrate and a third step of removing the transfer substrate. Due to the difference of the chemical affinity between the polymer layer and the transfer substrate on the one hand and the chemical affinity between the polymer layer and the micro-structured substrate on the other hand, the zones of the polymer layer, which are in contact with the micro-structured substrate during the second step, remain on the micro-structured substrate after the third step. These zones constitute the assembly joint.

BACKGROUND OF THE INVENTION

The invention relates to a method for production of a component,comprising a micro-structured substrate and a complementary elementassembled by means of an assembly joint. It also relates to a componentproduced by this method.

STATE OF THE ART

Production of micro-structured components, in particular micro-fluidicdevices (biochips, lab-on-chip, etc.) or micro electro-mechanicaldevices (MEMS, MOEMS, etc.), generally involves surface or volumemicro-structuring of at least one substrate where free spaces arecreated enabling fluids to circulate or to be stored. The cavities andchannels thus created are open on at least one side and therefore haveto be connected or assembled to another structure (open or closed cover,capillaries, other micro-fluidic substrate.).

Assembly of micro-structured components requires assembly joints andseals that may be micro-structured. However, handling and positioning ofmicro-structured joints is very difficult. Techniques exist using inparticular Polydimethylsiloxane as assembly joint, with complex methodsto define the surface of the joint. Other assembly techniques exist forsubstrates whose assembly surfaces may be locally very small, but thesetechniques require high temperatures or chemical preparations limitingthe possibility of functionalizing the components to be assembled (forexample by biological grafting) and are restrictive in the choice ofmaterials. In the field of polymer assembly, thermal welding also limitsthe choice of materials. The use of pre-glued adhesive films presentsthe drawback of the presence of glue in contact with fluids to behandled and gives rise to problems of biological compatibility.

More conventional gluing techniques (glue distribution by syringe, padprinting, glue rollers, screen printing), apart from the problemsrelated to polymerization of liquid glues in the presence of biologicalspecies, prove unsuitable for assembly of micro-structures presentingvery small assembly surfaces (<20 μm).

Known assembly techniques thus give rise to problems of biologicalcompatibility and/or are complex, which limits the applicationpossibilities. In addition, certain techniques do not enable reversibleassembly of two components.

OBJECT OF THE INVENTION

It is one object of the invention to remedy these drawbacks and, moreparticularly, to propose a method for production of micro-structuredcomponents minimizing the problems of biological compatibility, whilereducing the complexity and manufacturing cost.

According to the invention, this object is achieved by the fact that themethod comprises fabrication of the assembly joint by:

a first step of deposition of a thin layer of polymer on a transfersubstrate, the transfer substrate and the thin polymer layer having apredetermined chemical affinity,

a second step of bringing the micro-structured substrate and the thinpolymer layer into contact, the micro-structured substrate and the thinpolymer layer having a greater chemical affinity than the chemicalaffinity between the transfer substrate and the thin polymer layer,

a third step of removing the transfer substrate, so that the assemblyjoint is formed by the zones of the thin polymer layer coming intocontact with the micro-structured substrate in the course of the secondstep.

According to a preferred embodiment, the transfer substrate is flexibleand removal of the transfer substrate is performed by pulling the lattervia one end.

According to a development of the invention, the method comprises a stepof chemical activation of the complementary element and/or, after thethird step, a step of chemical activation of the assembly joint arrangedon the micro-structured substrate. An irreversible assembly of themicro-structured substrate and of the complementary element can thus beachieved.

It is another object of the invention to provide a component, producedby the above method, and comprising a complementary element assembled tothe micro-structured substrate by the assembly joint, the element beinga cover, another micro-structured substrate, a capillary or a matrix ofcapillaries secured to one another.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become more clearly apparent from thefollowing description of particular embodiments of the invention givenas non-restrictive examples only and represented in the accompanyingdrawings, in which:

FIGS. 1 to 6 represent different steps of a particular embodiment of amethod according to the invention.

FIG. 7 represents a particular embodiment of the invention with bearingzones on the micro-structured substrate.

FIG. 8 represents a particular embodiment of a component according tothe invention, wherein the complementary element is a capillary.

FIG. 9 represents an alternative embodiment of a transfer substrate.

DESCRIPTION OF PARTICULAR EMBODIMENTS

In a first step of the process represented in FIGS. 1 to 6, a thin layerof polymer 2 is deposited on a transfer substrate 1. A typically useddeposition technique is spin coating. The polymer of the thin layer 2and the material of the transfer substrate 1 must have a chemicalaffinity enabling the second and third steps described hereafter. In apreferred embodiment, the materials of the transfer substrate 1 and ofthe thin polymer layer 2 are both Polydimethylsiloxane (PDMS). Oneadvantageous property of a PDMS transfer substrate 1 is its flexibility.Depending on the polymer used for the thin layer 2 and on the depositiontechnique, an additional intermediate cross-linking step, for example byheating, can be added just after deposition.

The second step (FIG. 3) consists in bringing the thin polymer layer 2,supported by the transfer substrate 1, into contact with themicro-structured substrate 3. The chemical affinity between the thinpolymer layer 2 and the micro-structured substrate 3 must be greaterthan the chemical affinity between the thin polymer layer 2 and thetransfer substrate 1. Adjustment of the chemical affinity between thethin polymer layer 2 and the micro-structured substrate 3 can beperformed, before the second step, by additional intermediate chemicalactivation steps. As represented in FIG. 2, the chemical activationsteps can be applied to the polymer layer 2 and/or to themicro-structured substrate 3. A chemical activation means used is anoxygen plasma. In FIG. 2, simultaneous plasma oxidizing of the thinpolymer layer 2 and of the micro-structured substrate 3 is represented.Moreover, the tenacity of the thin polymer layer 2 decreases after theplasma oxidizing, facilitating the third step of the method describedbelow. The thin polymer layer can be irreversibly glued to themicro-structured substrate by suitably adjusting the chemical affinityby chemical activation steps before the second step (FIG. 2).

In a third step, the transfer substrate 1 is removed. Only the zones ofthe thin polymer layer 2 in contact with the micro-structured substrate3 during the second step remain on the micro-structured substrate 3. Asthe chemical affinity between the micro-structured substrate 3 and thethin polymer layer 2 is greater than the chemical affinity between thethin polymer layer and the transfer substrate 1, the thin polymer layer2 in fact tears, a part 4 remaining fixed to the micro-structuredsubstrate 3, the rest 6 being removed with the transfer substrate 1. Thezones of the thin polymer layer 2 that were not in contact with themicro-structured substrate 3 during the second step thus remain asresidues 6 on the transfer substrate 1. The assembly joint 4 is thusformed by the zones of the thin polymer layer 2 remaining on themicro-structured substrate 3. In the case of a flat transfer substrate1, the second step does not require any alignment, the micro-structuredsubstrate 3 itself defining the contact zones with the thin polymerlayer 2. For the thin polymer layer to tear at the edge of the patternsmachined in the micro-structured substrate 3, the tenacity of the thinpolymer layer 2 must be very weak. The tenacity can be reduced inparticular by plasma oxidizing prior to the second step (FIG. 2).

The method described above enables an assembly joint 4 to be formedhaving the same shape as the micro-structured substrate 3 to beconnected or assembled, without leaving any dead volume and withoutadding any matter above cavities 5 formed in the micro-structuredsubstrate 3. The surface of the assembly joint 4 in contact with thematerials (fluids, liquids, etc.) contained in the cavities 5 istherefore minimized, which enables a possible interaction between thematerial of the assembly joint 4 and the materials contained in thecavities 5 to be attenuated. The biological compatibility of thecomponent is thus optimized.

This method enables a multitude of micro-assembly joints to be formedsimultaneously, each joint being able to be very small (<20 μm), onmicro-structured substrates of large surface (treatment of a completewafer), the micro-structured substrate itself confining the assemblyjoint. The method is quick, inexpensive and does not require anyalignment for formation of the joints.

In a preferred embodiment, execution of the third step is facilitated bythe use of a flexible transfer substrate that can be removed via one end(FIG. 4). This makes it possible to avoid using too great a force thatmight damage the component.

After the third step, a complementary element 7 can be fixed onto themicro-structured substrate 3 by means of the assembly joint 4, possiblyin reversible manner, securing the complementary element 7 by means of adevice (not shown) ensuring an intimate contact with the assembly joint4. It is also possible to fix the complementary element 7 inirreversible manner on the micro-structured substrate 3 by adding one ormore chemical activation steps of the assembly joint 4 and/or of thecomplementary element 7, for example by plasma oxidizing (FIG. 5). Acomponent obtained in this way, comprising a micro-structured substrate3 and a complementary element 7 assembled by means of an assembly joint4, is represented in FIG. 6.

In a particular embodiment, represented in FIG. 7, the micro-structuredsubstrate 3 comprises a bearing zone 8 acting as bearing surface for thetransfer substrate 1 in the course of the second step in the case wherezones designed to define the assembly joint 4 are located relativelydistant from one another. The bearing zones 8 thus prevent the thinpolymer layer 2 from sticking on the bottom surfaces 9 of themicro-structured substrate 3 comprised between two zones defining theassembly joint, while ensuring the parallelism between the transfersubstrate and the micro-structured substrate during the second step.

In the alternative embodiment represented in FIG. 6, the complementaryelement 7 is a cover 7 closing the cavities 5 of the micro-structuredsubstrate 3. According to another particular embodiment of theinvention, represented in FIG. 8, the complementary element is formed bya capillary 10 or a matrix of capillaries secured to one another. Inanother embodiment, the complementary element 7 is anothermicro-structured substrate.

In a particular embodiment, represented in FIG. 9, the transfersubstrate is a micro-structured substrate 11 enabling contact of thethin polymer layer 2 to be prevented on certain zones 12 of the surfaceof the micro-structured substrate 3. Formation of a micro-structuredtransfer substrate 11 of this kind can be achieved by molding forexample. However, unlike a flat transfer substrate, a micro-structuredtransfer substrate 11 requires an alignment with the micro-structuredsubstrate 3 during the second step of the method, making the method morecomplicated.

The material of the assembly joint is to be chosen from amongthermo-hard resins, elastomers or elastomer thermoplastics meeting thefollowing criteria:

-   -   being sufficiently flexible once the joint is formed to perform        its tightness and assembly function, enabling for example        roughness or flatness defects of the micro-structured substrate        to be compensated (visco-elastic behavior),    -   forming covalent bonds with the micro-structured substrate and        the transfer substrate, after suitable treatment if required,    -   having a low tenacity, after suitable treatment if required, so        as to tear easily when transfer takes place. The above-mentioned        polymer families see their tenacity decrease over a depth        generally of 100 μm to 150 μm after plasma oxidizing. As the        thickness range of the joint described is smaller, it will be        oxidized and therefore made fragile over its whole depth, thus        rendering the transfer operation easier,    -   preferably, being available in liquid form to be able to be        spread by spin coating.

Polydimethylsiloxane (PDMS), and more particularly Sylgard® 184 gradefrom Dow Corning®, is particularly suitable, notably on account of itsoptic and biological compatibility qualities. Dow Corning® Sylgard® 184grade PDMS can be activated by a low-energy oxygen plasma (creation ofSiOH and OH sites; hydroxylation) enabling it to be irreversibly stuckto silicon, to glass, to a wide range of plastics, to itself, etc. It isavailable in non cross-linked form, supplied along with a hardener, andtherefore sufficiently liquid to be spread by spin coating. Surfacehydroxylation could be performed by plunging the selected polymer intoboiling water. This method does however prove less simple to implement.

The transfer substrate material is preferably chosen to be able to formcovalent bonds (free methacryl groups for example, which bond with themethacryl groups of the thin layer PDMS) with the assembly jointmaterial and for its flexibility. For this reason, a preferable choiceis a transfer substrate made from PDMS, freshly fabricated to avoid anyproblem of dust collection related to storage, as PDMS is very fond ofdust.

The thin layer of PDMS is preferably hot cross-linked to save time (4hours at 60°). The use of a spin-coating-whirler enables the thicknessof the assembly joint to be chosen (typically between a few micrometersand 50 μm).

The material of the micro-structured substrate to be assembled orconnected, or at least of the surfaces dedicated to formation of theassembly joint, must be able to be activated to form covalent bonds withsaid assembly joint. Likewise, covalent bonds can be achieved betweensaid joint and the complementary element. Under these conditions, theassembled final component can be fluid-tight.

In fabrication of enzymatic digestion reactors on silicon, themicro-structured substrate is composed of channels with a length ofseveral millimeters and a width of 1 mm wherein matrices of columns witha diameter of 5 μm or 10 μm are micro-machined (several millioncolumns). This enables the surface/volume ratio of said reactors to beincreased, the enzymatic digestion reaction taking place between enzymesgrafted on the walls and proteins conveyed in these reactors.

The present invention, as described above, has notably enabled anassembly joint to be formed on very small patterns (square columns with5 μm sides and hexagonal columns with a diameter of 10 μm), and onrelatively large surface components (4×2 cm²), without any dead volumeabove these columns, while minimizing the surface of PDMS facing thefluids (problems of protein adsorption on the PDMS).

1-16. (canceled)
 17. Method for production of a component, comprising amicro-structured substrate and a complementary element assembled bymeans of an assembly joint, method comprising fabrication of theassembly joint by: a first step of deposition of a thin layer of polymeron a transfer substrate, a second step of bringing the micro-structuredsubstrate and the thin polymer layer into contact, a third step ofremoving the transfer substrate so that the assembly joint is formed bythe zones of the thin polymer layer coming into contact with themicro-structured substrate in the course of the second step, methodwherein the transfer substrate is flexible and removal of the transfersubstrate is performed by pulling the latter via one end, themicro-structured substrate and the thin polymer layer having a greaterchemical affinity than the chemical affinity between the transfersubstrate and the thin polymer layer.
 18. Method for productionaccording to claim 17, comprising a cross-linking step of the thinpolymer layer between the first and second steps.
 19. Method forproduction according to claim 17, comprising a chemical activation stepof the thin polymer layer deposited on the transfer substrate betweenthe first and second steps.
 20. Method for production according to claim17, comprising a chemical activation step of the micro-structuredsubstrate between the first and second steps.
 21. Method according toclaim 17, wherein the transfer substrate is made fromPolydimethylsiloxane (PDMS).
 22. Method according to claim 17,comprising, after the third step, a chemical activation step of theassembly joint arranged on the micro-structured substrate.
 23. Methodaccording to claim 17, comprising a chemical activation step of thecomplementary element.
 24. Method according to claim 17, wherein themicro-structured substrate comprises at least one bearing zone acting assupport for the transfer substrate in the course of the second step. 25.Method according to claim 17, wherein the transfer substrate is flat.26. Method according to claim 17, wherein the transfer substrate ismicro-structured.
 27. Method according to claim 17, wherein the polymermaterial of the thin polymer layer is chosen from among thermo-hardresins, elastomers and elastomer thermoplastics.
 28. Method according toclaim 27, wherein the polymer material of the thin polymer layer isPolydimethylsiloxane (PDMS).
 29. Component, produced by the methodaccording to claim 17, wherein the complementary element is a cover. 30.Component, produced by the method according to claim 17, wherein thecomplementary element is another micro-structured substrate. 31.Component, produced by the method according to claim 17, wherein thecomplementary element is a capillary or a matrix of capillaries securedto one another.